There are many types of high frequency selecting switches presently in use. The switch shown in FIG. 4 has been commonly used in prior art. At the rear end of the switch are three co-axial terminals (a1, a2, and a3). Both of the side terminals (a1 and a3) are connected to the input signal cables respectively and the middle terminal (a2) is connected to the output signal cable. Two selection buttons (A and B) are disposed at the front end of the switch. If, for example, button (A) is pressed, then input terminal (a1) is connected to the output terminal (a2), with the other terminal (a3) being in an open state. Terminal (a3) sometimes receives unwanted signals from the surroundings which interfere with the output signal. In order to prevent this interference, a plug (C) was often disposed on the unused input terminal. The plug (C) has a resistor, which is connected between the housing of the plug (C) and the center conductor line of the terminal, so as to absorb any undesirable signals from the surroundings, thereby preventing interference. It is obvious that the above-mentioned design has complicated operation and testing functions and is uneconomical to manufacture.
There is another type of high frequency selecting switch which is an improvement of above-mentioned type. Referring to FIG. 5, it can be seen that the side terminals (i.e. the input signal terminals) are equipped with resistors D and D'. This design does absorb undesirable signals from the surroundings so as to prevent interference and to provide more convenient operation. However, the design shown in FIG. 5 is more difficult and expensive to manufacture. Further, this design is too bulky.